dental materials
TRANSCRIPT
Overseas Registration Exam
Dr.Sayij M,B.D.S, I.Q.E, M.D.S
SILVER AMALGAMDefinition: An amalgam is a special type of alloy in which one of its constituents is mercury. Before these alloys (metal) combine with mercury they are known as dental alloys.
Historically Amalgam alloys containedAg - 65% Tin - 29% Cu < 6%
During the 70s amalgam alloys containing between 6 and 30 % were produced High Copper Alloys
Shape and method of production of alloy particlesA cast ingot of the alloy is passed through a lathe machine Lathe-cut alloy A cast ingot is milled Milled alloy Molten alloy is sprayed into a column of inert gas and solidify as fine droplets of alloy Spherical alloy
Hence the alloy powder can be supplied as either:1.
2.3.
Lathe-cut Spherical particles Admixed (varying size & shape of particles; better packing efficiency) AND
High copper alloys
Single-composition, Cu enriched alloys High Cu alloys similar in shape and size and have same chemical composition Admixed alloy Combination of lathe-cut low copper and spherical Ag-Cu eutectic alloy
Particle size
Modern powders particle size 15-35m Small particle size < 3 m es the surface area of powder thus requires more Hg Current trend use smaller particle size powders for rapid hardness with greater early strength
Setting reactions of conventional alloysAg3Sn + Hg( Gamma + Hg1.2.
Ag2Hg3 + SnHgGamma 1 +
+
Ag3Hg
Gamma 2 + Gamma )
Ag3Sn
Gamma
Ag2 Hg3 Gamma 1
3.
SnHg
-- Gamma 2 (weakest phase)
* Copper is added to eliminate the gamma 2 phase.
* Gamma 2 phase is least stable in corrosive environment * In a high copper system, gamma 2 phase is virtually eliminated by the (Cu-Sn phase) and to accomplish this at least 12 % copper is required in the alloy powder
COMPOSITION OF MODERN AMALGAM POWDER SILVER (40% min) TIN (32% max) COPPER (30% max) ZINC (2% max) MERCURY (3% max , used in pre-amalgamated alloys) Sometimes, traces of Indium and Palladium COMPOSITION OF MERCURY Hg is purified by distillation
Role of Copper
To eliminate the weakest (tin-Hg or gamma-2) phase in amalgam the content of copper is increased Copper therefore hardens and strengthens the amalgam.
Role of zinc :
Scavenges the available oxygen to stop oxidisation of Ag, Sn or Cu during the melting of the alloy. Zinc-containing alloy > .01 % Non-zinc containing alloy .01 % Alloys without zinc are brittle and less plastic Prevents early corrosion and enhances marginal integrity Disadvantage : it causes an abnormal expansion if amalgam is condensed in presence of moisture
Spherical vs Lathe-cut vs Admixed
Amalgams with lesser Hg content have better properties Spherical alloys have smaller surface area and hence require lesser mercury Spherical alloys give a more fluid mix, easy to condense and can be carved immediately Spherical alloys preferred for Class V and pinned restorations.
Contd.
Because they are very plastic establishing proximal contours is difficult Admixed alloys resist condensation better Spherical alloys occlusal strength 3hr Lathe-cut alloy occlusal strength > 6hr
Lifetime of AmalgamMaterial
Dentist
Patient
Factors governing quality
By Dentist Selection of alloy Mercury-alloy ratio Trituration Condensation Anat. characteristics Marginal integrity Final finish
By manufacturer Composition Heat treatment Size, shape and method of production Surface treatment Form in which supplied
Dimensional change
Severe contraction microleakage and caries Expansion pressure on pulp and may cause post-operative sensitivity Hg, condensation pressures and longer trituration time will favour contraction
Effect of moisture contamination
Some admixed alloys expand upto 2 yrs If zinc containing alloy is contaminated during trituration or condensation expansion starts 35 days later and may continue for months, sometimes > 4 % - DELAYED EXPANSION
STRENGTH
Weaker in tension and stronger in compression Single
composition (strongest)
Admixed High copper amalgam.
Effect of mercury content
Too less or too much weakens amalgam Should be sufficient to wet alloy powder otherwise a dry granular mix results If Hg content es above 54-55 % the strength rapidly reduces Excess Hg also causes more formation of the weak gamma 2 phase (weak phase)ALLOY : MERCURY VARY BETWEEN 5:8 AND 10:8
For optimum properties, set amalgam should contain lee than 50% mercury
Condensation and Porosity
Lathe-cut needs greater pressure Spherical needs lighter pressure condensation pressure will porosity and the strength
Properties
Compressive strength: at 1 hr.. 50 MPa (minimum) at 24hr. 300 MPa (minimum)(enamel cusp is 250 MPa)
Creep: 3% (maximum) much less for copper-enriched Tensile strength: at 7 days 60 MPa (enamel cusp is 35 MPa) but still very brittle and weak in thin sections. Need about 2mm thickness of amalgam Dimensional change : - 0.1% to +0.2%
Contd.
Corrosion :
more gamma 2-- more corrosion; copper enriched less corrosion; when in contact with gold corrosion is accelerated due to large difference in potential
Tarnish:
loss of surface lustre due to formation of sulphide layer
Thermal diffusivity:
78 x 10 units (while dentine is 2 x 10)
Coefficient of thermal expansion:
25 x 10 units (dentine 8 x 10) three times more than dentin. Amalgam contracts and expands more than dentine when subjected to thermal changes
Condensation pressure:3-4 pounds
Disadvantages of Amalgam
Allergy Galvanism Delayed expansion Plaque accumulation Poor esthetics Lack of chemical bond
BIOHAZARDS OF AMALGAM ???
Micro-mercurial poisoning Micro-leakage Thermal conductivity Polishing - release of mercury Bruxism - release of mercury Replacement - release of mercury Mercury found in pulp post amalgam condensation
Still widely used
Used for over 80 years in the UK Excellent track record Studies are longer for amalgam 20 million fillings placed or replaced in one year
Release of mercury in practice ..30 g /m3 could be released during a clinical session Urinary levels for dentists 2.18 moles mercury/mole creatinine Urinary levels for nurses 2.26 moles mercury/mole creatinine It means: 0-5 Band A Normal for occupation 5-10 Band B some exposure 10-20 Band C significant exposure > 20 Band D exceeds HSE Health Guidance Value
Mercury poisoning
Forms - Metal (Hg0) shows absorption~ 0.01% - Inorganic ion (Hg) shows absorption ~ 1-7% - Organic (methyl or ethyl mercury) have absorption ~ 90% Access to body Skin, Vapour, Gut
Mercury toxicity :
Paraesthesia - ~500g/kg Ataxia Joint pain Death - ~ 1000 g/kg - ~ 2000 g/kg - ~ 4000 g/kg
Mercury in amalgam
About 1 3 g/day as amalgam particulate Hg0 Parafunctionists, ingestion ~45 g/day as amalgam particulate or Hg+ But the gut absorption is about 1-7 % Half-life is about 20-90 days Fish consumption is about 4 g/day of methyl mercury (absorption > 90%) Intake from all sources other than amalgam ~20 g/day of Hg+
Cary Bopiah
Levels needed from dentistry for MINIMAL observable effect ... * 450-530 amalgam surfaces to give a urine mercury level of 30 g/g creatinine * If all teeth were restored - - only 192 surfaces
Recommendations
An average of 5 amalgams a year is unlikely to cause mercury poisoning Mercury released from a normal number of surfaces unlikely to cause any poisoning Pregnant patient should not take part in removal or replacement of amalgam fillings Not advisable to replace amalgam with non-amalgam if the reason is one of suspected mercury poisoning
Bonded amalgam restorationsAn auto-polymerizing dentine bonding agent is coated then amalgam placed in cavity. Panavia Scotch bond All bond 2 Amalgam bond plus Advantages Less tooth structure removed Increased fracture resistance Easy repair of ditched or fractured amalgam
Longevity of RestorationsMaterial Amalgam (I,II,V) Range (yrs)5-25 3-10
Adjusted11 6
mean
Ant. CompositesPost. Composites
3-9 3-5 10-25 10-25
5 6 17 18
Glass Ionomer Cast high noblePorcelain fused to metal
Composites : .. are resins consisting of organic and inorganic phases bonded by a coupling agent.
COMPOSTION :
RESIN - BISGMA - UDMA - plus TEGDMA (to reduce viscosity of resin and to allow
fillers to be added to resin)
FILLERS
-
Quartz Glass
: conventional composites (1-5 m) : conventional composites (aluminosilicate or borosilicate) (1-5 m) Fused silicon : microfilled (0.4 m)
Uses of filler: To increase strength Increase abrasion resistance Decrease polymerization shrinkage Better polishability
Composition Contd..
Coupling agent : Silane (coats filler particles to enhance bond between resin matrix and fillers) Opacifier : Barium oxide Initiator : Benzoyl peroxide Photo initiator : Camphoroquinone
Classification 1. 2. 3.
According to filler size Macrofilled quartz or glass Microfilled silica Hybrid quartz or glass + silica (80-90% by weight) Macro have better strength and mechanical properties (60-80% by weight) Micro have better polishability, lesser strength Hybrid intermediate qualities
Classification (contd.)
According to method of curing: Chemically cured Light cured Dual cured
GLASS IONOMERS
Generally known to be an IRM (intermediate restorative material) Only restorative material that truly bonds to tooth surface Water based and hence hydrophilic
Types of GIC
Type I Luting Type II restorative Type III lining Type IV - Light cure and Dual cure
Composition
Aluminosilicate glass + polyalkenoic acid Resin modified GIC HEMA is added
Properties
Adhesion to enamel and dentin, there is ionic displacement of Ca and Po4 ions by polyacrylate ions and adsorption of polyalkenoic acids onto collagen Cariostatic due to fluoride release Thermal expansion similar to enamel and dentin Radiolucent except ketac-bond Abrasion resistance is poor Biocompatibility good (not resin modified GIC) Polyacrylic acid is mild and molecule is large and cannot diffuse into dentinal tubule
Contra-indicated
High stress bearing areas Esthetic areas Large class II and IV
IMPRESSION MATERIALS :
IMPRESSION MATERIALS
NON ELASTIC POP Imp. Compound ZOE paste Wax
ELASTOMERS Silicone (add, cond) Polysulphides Polyethers
HYDROCOLLOIDS Reversible Irreversible
COMPOSITION OF ALGINATE
K or Na alginate reacts with water to form a solution Calcium sulfate reactor Diatomaceous earth filler Trisodium phosphate retarder Potassium titanium fluoride accelerator Zn oxide - filler
USES OF ALGINATE
Bleaching trays, mouthguards RPD, crown and bridge Ortho study casts Mouth protectors for sportsmen
Problems with alginate
Sticks to teeth Voids in impression Tears during removal Lack of detail Grainy appearance Early setting Pulls away from tray
ELASTOMERSTYPES: Polysulfide Silicones : Addition and Condensation Polyether ADDITION SILICONES (Reprosil, Aquasil) Base Poly methyl hydrogen siloxane (PMHS) and fillers Reactor divinyl polydimethyl siloxane (DPDS) and fillers
Elastomers (contd.)Advantages : Addn. silcn Dimensionally stable Easy manipulation Most elastic of all impression materials Multiple pours possible Compatible with gypsum products Long shelf life
Elastomers (contd.) Disadvantages: Addn. silcn Latex inhibits reaction Hydrophobic Hydrogen gas evolution (wait 1 hr before pouring) Low tear strength
Mineral Trioxide Aggregate (MTA)Composition: Calcium oxide Zinc oxide Aluminium oxide
Uses Pulp capping Perforation repair Apexification Root end restoration after apicectomy
DENTAL CEMENTSLUTING LINING FILLING
GIC ZnPo4
Varnish GIC
ZOE GIC
Zn polycarboxylate
Calcium hydroxide
Composite based luting cement
Ideal requirements :
Healing of pulp dentin organ Sedative action Seal dentinal tubules Provide insulation Dentin bridge formation
Zn Oxide Eugenol Cement
Powder Zn Oxide Liquid Eugenol Resin bonded ZOE 10 % hydrogenated powder added (HEMA) Weakest cement eugenol is an obtundent, has analgesic action Antiseptic and anti-inflammatory Contraindicated under resins (interferes with polymerization)
Calcium Hydroxide
Powder CaOH2 + fillers Liquid polysalicylate fluid Or base paste +catalyst paste Ph is 11 Bacteriostatic can induce mineralization of adjacent pulp Uses- pulp capping, perforations, root canal medicament, apexification,lining
Zn Phosphate
Powder Zn oxide and Mg oxide Liquid 50 % phosphoric acid Always use varnish underneath Advantage good strength, good adaptability, best insulator Disadv irritant to pulp, exothermic reaction
Zn Polycarboxylate
Powder Zn oxides and Mg oxides Liquid 40 % aqueous polyacrylic acid Similar to ZnPo4, good strength, good insulator Difficult to handle(eg.mixing)
Dental PorcelainPorcelain refers to a family of ceramic materials composed essentially of Kaolin, Feldspar, Quartz fired at a high temperature Other constituents fluxes, colour pigments, opacifying agents, stains, colour modifiers
Properties
Chemically stable Excellent compressive strength 350-500 mpa Thermal conductivity and coefficient of expansion similar to dentin Biocompatible Minimal plaque accumulation Excellent esthetics
Types of CeramicsHigh fusing 1300 C Medium fusing 1101-1300 C Low fusing 850-1100 C Ultra low fusing